Ink set and printing apparatus

Abstract

An ink set including a first ink containing a pigment and a water-soluble resin having an anionic group, a second ink containing substantially no pigment and a reactive component, and a third ink containing a polymer emulsion and a water-soluble resin having an anionic group. The pKa of the reactive component is lower than the pKa of the anionic group of the water-soluble resin in the first ink and higher than the pKa of the anionic group of the water-soluble resin in the third ink.

What is claimed is: 
     
       1. An ink set comprising different inks having different functions, the inks including:
 a first ink containing a pigment as a coloring material, and a water-soluble resin having an anionic group; 
 a second ink containing substantially no coloring material and a reactive component reactive with the first ink; and 
 a third ink containing substantially no coloring material, a polymer emulsion, and a water-soluble resin having an anionic group, 
 wherein the pKa of the reactive component in the second ink is lower than the pKa of the anionic group of the water-soluble resin in the first ink and higher than the pKa of the anionic group of the water-soluble resin in the third ink so that the pigment in the first ink in combined use with the second ink is more flocculable than the polymer emulsion in the third ink in combined use with the second ink. 
 
     
     
       2. The ink set according to  claim 1 , wherein the reactive component in the second ink is an organic acid. 
     
     
       3. The ink set according to  claim 2 , wherein the reactive component in the second ink is glutaric acid. 
     
     
       4. The ink set according to  claim 1 , wherein the water-soluble resin in the third ink has a sulfo group or a phosphate group. 
     
     
       5. The ink set according to  claim 1 , wherein the water-soluble resin in the first ink has a carboxy group. 
     
     
       6. The ink set according to  claim 1 , wherein the polymer emulsion in the third ink forms a coating film when being heated. 
     
     
       7. The ink set according to  claim 1 , wherein the pigment in the first ink in combined use with the second ink is more flocculable than the polymer emulsion in the third ink in combined use with the second ink. 
     
     
       8. The ink set according to  claim 1 , wherein the precipitation value of the pigment in the first ink in combined use with the second ink is higher than 0.1, and the precipitation value of the polymer emulsion in the third ink in combined use with the second ink is less than 0.1. 
     
     
       9. The ink set according to  claim 1 , wherein the difference in pKa between the anionic group of the water-soluble resin in the first ink and the reactive component in the second ink is 0.5 or more. 
     
     
       10. A printing apparatus, comprising:
 a printing head configured to eject different inks having different functions, the inks including a first ink containing a pigment as a coloring material and a water-soluble resin having an anionic group, a second ink containing substantially no coloring material and a reactive component reactive with the first ink, and a third ink containing substantially no coloring material, polymer emulsion, and a water-soluble resin having an anionic group, wherein the pKa of the reactive component in the second ink is lower than the pKa of the anionic group of the water-soluble resin in the first ink and higher than the pKa of the anionic group of the water-soluble resin in the third ink so that the pigment in the first ink in combined use with the second ink is more flocculable than the polymer emulsion in the third ink in combined use with the second ink; and 
 a controller configured to control an ejection of the inks from the printing head onto a printing medium. 
 
     
     
       11. The printing apparatus according to  claim 10 , wherein the controller controls the ejection so that printing is performed while the printing head scans a unit area of the printing medium a plurality of times. 
     
     
       12. The printing apparatus according to  claim 11 , wherein the controller controls the ejection so that the second ink is ejected with a higher proportion than the first ink in an earlier time of the plurality of times of scanning. 
     
     
       13. The printing apparatus according to  claim 12 , wherein the controller controls the ejection so that the first ink is not ejected before the first scanning of the plurality of times of scanning and the second ink is not ejected after the first scanning of the plurality of times of scanning. 
     
     
       14. The printing apparatus according to  claim 11 , wherein the controller controls the ejection so that the third ink is ejected with a higher proportion than the first ink in a later time of the plurality of times of scanning. 
     
     
       15. The printing apparatus according to  claim 14 , wherein the controller controls the ejection so that the third ink is not ejected before the second scanning of the plurality of times of scanning and the first ink is not ejected after the second scanning of the plurality of times of scanning. 
     
     
       16. The printing apparatus according to  claim 10 , wherein the reactive component in the second ink is an organic acid. 
     
     
       17. The printing apparatus according to  claim 16 , wherein the reactive component in the second ink is glutaric acid. 
     
     
       18. The printing apparatus according to  claim 10 , wherein the water-soluble resin in the third ink has a sulfo group or a phosphate group. 
     
     
       19. The printing apparatus according to  claim 10 , wherein the water-soluble resin in the first ink has a carboxy group. 
     
     
       20. The printing apparatus according to  claim 10 , wherein the polymer emulsion in the third ink forms a coating film when heated. 
     
     
       21. The printing apparatus according to  claim 10 , wherein a precipitation value of the pigment in the first ink in combined use with the second ink is higher than 0.1, and a precipitation value of the polymer emulsion in the third ink in combined use with the second ink is less than 0.1. 
     
     
       22. The printing apparatus according to  claim 10 , wherein a difference in pKa between the anionic group of the water-soluble resin in the first ink and the reactive component in the second ink is 0.5 or more. 
     
     
       23. The printing apparatus according to  claim 10 , further comprising ink tanks storing the respective different inks fed to the printing head. 
     
     
       24. An ink set comprising different inks having different functions, the inks including:
 a first ink containing a pigment as a coloring material, and a water-soluble resin having an anionic group; 
 a second ink containing substantially no coloring material and a reactive component reactive with the first ink; and 
 a third ink containing substantially no coloring material, a polymer emulsion, and a water-soluble resin having an anionic group, 
 wherein the reactivity between the reactive component in the second ink and the anionic group of the water-soluble resin in the first ink is higher than the reactivity between the reactive component in the second ink and the anionic group of the water-soluble resin in the third ink.